Packaging method using elastic memory foam as safety indicator for heat damage

ABSTRACT

An open cell foam with thermal memory characteristic is used as an indicator for heat damage to an article containing heat sensitive contents packaged in a carton. The foam material may be a polyurethane-based thermoplastic polymer referred to as “Cold Hibernated Elastic Memory” (CHEM) foam. The thermal memory foam can be produced in compressed form and used as inserts in the carton. Upon exposure to a temperature at or above the foam glass transition temperature, the foam insert expands to substantially its original shape (volume) so as to apply a compressive force against the article, making it difficult to remove from the carton. Alternatively, the expanded foam will deform the carton walls, providing an external indication of heat damage. The foam can also be used as a heat-indicating element in an inspection panel of the carton, which ruptures so as to provide external indication of heat damage.

PRIORITY CLAIM

[0001] This application claims the priority date of, and incorporates byreference, pending U.S. Provisional Patent Application No. 60/256,239,which was filed on Dec. 15, 2000.

TECHNICAL FIELD

[0002] This invention generally relates to the use of foam materials forpackaging applications, and more particularly, to the use of elasticmemory foam for detection of heat damage to the carton contents.

BACKGROUND OF INVENTION

[0003] Foam materials have been widely used for thermal insulation andshock absorption in packaging of fragile or heat sensitive contents. InU.S. Pat. No. 3,420,363 to Blickensderfer, methods for forming and usingopen-celled foam materials having “thermal memory” are disclosed. Foamsfound to have thermal memory characteristics include those produced frombutadiene liquid polymer and suitable amounts of an activator and sulfurmonochloride. The foam materials can be foamed, heated to a softenedstate, compressed and cooled to a densified state of about 20% itsoriginal volume in which it can be worked, then subsequently heated toan elevated temperature of about 150° F. to 300°F. to re-expand the foamto its original volume. In one application, the compressed foam can belaminated or adhered to various packaging substrates or used as panelsor inserts in a carton, then re-expanded to form a snug, shock-absorbingcushion for an article packaged in the carton. In another application,the article is wrapped in a sheet of densified foam and inserted in anenclosing carton, then the foam is re-expanded to immobilize and cushionthe article in the carton. In yet another application, the densifiedfoam can be incorporated in a structure of reduced volume, to facilitatetransportation, then re-expanded to its greater volume at the point ofuse.

[0004] Recently, a new class of open cellular foam materials have beendeveloped for space applications at the Jet Propulsion Laboratory,California Institute of Technology, Pasadena, Calif., in conjunctionwith Nagoya R&D Center, Mitsubishi Heavy Industry, Nagoya, Japan. Thesefoam materials are described in the proceedings of SPIE '99International Symposium on Smart Structures and Materials, March 1999,Newport Beach, Calif., in an article entitled “Cold Hibernated ElasticMemory (CHEM) Self-Deployable Structures”, by W. Sokolowski, A.Chmielewski, S. Hayashi, and T. Yamada. The foam materials arepolyurethane-based thermoplastic polymers with a wide glass transitiontemperature Tg range. They can be compressed to as little as 5% of theiroriginal volume and re-expanded at the point of use. The material'smemory shape function allows repeated shape changes and shape retention.They are proposed for use as low weight, small volume materials in theirdensified state that are expandable for large, deployable spacestructures.

SUMMARY OF INVENTION

[0005] While the prior art has shown the use of thermal memory foammaterials as insulative and shock-absorbing packaging materials, and forthermal re-expansion to field-deployable larger volume structures, thepresent invention seeks to use the thermal memory characteristic of thefoam materials for other purposes, namely packaging safety applicationsas an indicator of heat damage or exposure to elevated or unacceptablehigh temperatures.

[0006] In accordance with a first preferred embodiment of the presentinvention, a method for packaging an article which containsheat-sensitive contents that may be damaged by heat above apredetermined threshold temperature Tt comprises: selecting an opencellular foam material having a thermal memory characteristic at a glasstransition temperature Tg which is approximately equal to or greaterthan the heat-damage temperature threshold of the contents of thearticle; forming the foam material to an original foamed volume OV;heating the foam material to a temperature greater than or equal to itsglass transition temperature Tg; compressing it at this elevatedtemperature to a selected densified volume DV; cooling the densifiedfoam material to a temperature below its Tg to retain it in thedensified state; applying the densified foam material around an articlein a carton leaving a free space in the carton which is defined as thequantity (OV−DV) multiplied by a “volume factor” Y. This free space maybe between the article and the foam material, or between the cartonwalls (side, top, bottom) and the foam material, or any combinationthereof. When heat is applied to the carton in such a manner that thefoam temperature exceeds its Tg, the foam material tends to re-expand tosubstantially its original volume OV, resulting in a visible or physicalindication that the package contents may have been exposed to atemperature above the predetermined threshold temperature.

[0007] If the design packaging system is such that volume factor Y isequal to or greater than 1, there will be visible indication ofpotential heat damage upon inspecting the interior of the package, asthe expanded foam will occupy a noticeable percentage of what wasoriginally free space inside the package. When volume factor Y is lessthan 1, the expanded foam will occupy essentially all of the availablefree space in the package, and will exert force upon either the packagecontents, the package walls, or, in most cases, both the contents andthe walls. In this case, the package walls will tend to bulge outward,providing rapid visual indication of exposure to elevated temperatures.If the stiffness of the package walls is such that they resistdeformation, the expanded foam will produce an inward force on thecontents of the package, making the removal of the contents difficult.In all cases and regardless of package wall stiffness, if Y is less than1, this inward force will be present to some degree and will tend tomake removal of package contents difficult without destroying thepackage.

[0008] As used herein, substantially its original volume shall mean avolume that is less than or equal to its original volume.

[0009] In accordance with another embodiment of the invention, a methodfor packaging an article which contains heat-sensitive is contents thatmay be damaged by heat above a predetermined threshold temperaturecomprises: selecting an open cellular foam material having a thermalmemory characteristic at a glass transition temperature Tg which isapproximately equal to or greater than the heat-damage temperaturethreshold of the contents of the article; forming the foam material toan original foamed volume OV; compressing it at an elevated temperatureabove its glass transition temperature Tg to a selected densified volumeDV; cooling the densified foam material to a temperature below its Tg toretain it in the densified state; applying the densified foam materialto a heat-damage-indicating panel located on a wall of the carton havingan inner surface adjacent the article and an outer surface visibleexternally of the carton which is rupturable by the re-expanded foammaterial applied to the heat-damage-indicating panel, such that when atemperature exceeding the glass transition temperature Tg is applied tothe carton and the foam material in the heat-damage-indicating panel,the foam material is re-expanded to substantially its original volume OVto rupture the outer surface of the panel and thereby indicate that thecontents of the article may be heat-damaged.

[0010] Other objects, features, and advantages of the present inventionwill be explained in the following detailed description of the inventionhaving reference to the appended drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0011]FIG. 1 is a diagram illustrating the thermal memory cycle oforiginal shape (volume), compaction to a densified shape (volume), andshape restoration of a cold hibernation elastic memory (CHEM) foammaterial used in the invention.

[0012]FIG. 2 is a schematic illustration of the use of densified foam aspacking material for a packaging safety application which provides botha physical and visual indicator of heat damage of the contents of apackaged article.

[0013]FIG. 3 is a schematic illustration of the use of densified foam aspacking material for a packaging safety application which provides avisual indicator of heat damage of the contents of a packaged article.

[0014]FIG. 4 is a photographic illustration showing carton packinginserts made of CHEM foam material in densified form and with itsoriginal volume restored around an article packed in a carton.

[0015]FIG. 5 is a schematic illustration of the use of densified foamlayer in a panel of a carton for a packaging safety application toindicate heat damage to the contents of a packaged article.

DETAILED DESCRIPTION OF INVENTION

[0016] The preferred open cellular foam material with thermal memorycharacteristic as used in the present invention is a polyurethane-basedthermoplastic polymer of the type described in the previously mentionedarticle entitled “Cold Hibernated Elastic Memory (CHEM) Self-DeployableStructures”, by W. Sokolowski, A. Chmielewski, S. Hayashi, and T. Yamada(Sokolowski Article). The CHEM foam material has a wide glass transitiontemperature Tg range that can be selected anywhere in the range from−158° F. to +158° F. (−70° C. to +700° C.). This range is suitable forusing the CHEM foam material as an indicator for heat damage to contentssuch as pharmaceuticals which can become denatured or chemically changedwhen exposed to heat above a heat-damage threshold temperature of about120° F. and higher. If it is desired to use a foam material as anindicator for heat damage to contents at a higher threshold temperature,other shape-memory foam materials may be used, such as those describedin U.S. Pat. No. 3,420,363 to Blickensderfer which have a glasstransition temperature in the range of 150° F. to 300° F. While theexamples described herein employ the CHEM foam material as a heat-damageindicator for pharmaceuticals, it is to be understood that theprinciples of the invention may be applied equivalently to other foammaterials having other glass transition temperatures suitable for othertypes of packaged contents.

[0017]FIG. 1 shows the thermal memory cycle of a CHEM foam material, asillustrated in the Sokolowski Article. The CHEM material is formed as afoam having an original shape with an open celled structure filling acertain original volume (OV) . By applying heat about 15-20° C. aboveits glass transition temperature Tg, the foam is heated to a pliable or“rubbery” state in which it can be compressed, compacted, or otherwiseshaped into a densified form. The densified volume (DV) of thecompressed or compacted CHEM foam can be as little as 5% or less of itsexpanded size. The heat is then removed and the foam cools below theglass transition temperature to retain its densified shape and volume, astate referred to as “hibernation”. In the densified, hibernation state,the foam can be handled and worked as packing or packaging materialaround a article, such as a bottle, vial, or carton of pharmaceuticalcontents. If the packaged article is subjected to heat such that thetemperature of the densified foam reaches or exceeds its glasstransition temperature, the densified foam re-expands and is restored tosubstantially its original shape and volume. If the heat is now removed,the restored shape will become rigidized in the glassy state insubstantially its original shape and volume. It is this cycle that isused in the present invention as an indicator for heat damage inpackaging safety applications.

[0018] Referring to FIG. 2, an example is shown of the use of thedensified CHEM foam as a packing material in a first packaging safetyapplication. In this application, the CHEM foam acts as both a physicaland visual indicator for heat damage of the contents of a packagedarticle by compressing against and holding the article with sufficientforce such that it cannot be readily removed from its package carton.The package carton has walls 20 to which inserts of densified foam 24 inthe hibernation state are adhered or laminated. The densified foam has adensified volume 26, designated as DV, which leaves a free space eitherbetween the walls 20 and foam inserts 24 or, as illustrated in FIG. 2,between the article 22 in the carton and inserts 24. This free space 32,which is the space available for unconstrained foam expansion within thepackage, is defined as (OV−DV)*Y. If the packaged article issubsequently exposed to heat, which results in the glass transitiontemperature of the foam being exceeded, such as during storage ortransportation, the foam re-expands and tends to be restored tosubstantially its original volume 30, designated as OV. The volumefactor Y in this example is less than 1 and is selected such that acompressive force F is exerted by the expanding foam 28 against thearticle 22, such that the article cannot be readily removed from thefoam/package system. This would indicate to the purchaser or consumerthat the article has been heat-damaged, so that they can avoid use ofthe article and return it to the vendor.

[0019] For sake of illustration, both the compacted foam inserts 24 andthe expanded foam 28 are shown in FIG. 2. If the article 22 in FIG. 2were not present in the package, and the densified foam was allowed toexpand without constraint, the foam would expand by an amount 31 equalto (OV−DV). With the article 22 present in the package, the expandedfoam will be constrained by an amount 33 which is equal to(OV−DV)*(1−Y).

[0020] Alternatively, the volume OV may be selected to exceed the freespace in the carton so as to cause the carton walls 20 to deform andbuckle outwardly. This would indicate to the inventory manager, stockingclerk, sales clerk or consumer that the packaged article has been heatdamaged. The dimensions of different types of cartons will vary widely.The CHEM foam is chosen and formed with predetermined original volume OVand subsequently densified to a volume DV depending on the particulardimensions and desired free space in the carton. Due to the highrigidity of the restored foam, the volume factor Y can be reliablyselected by calculation of the desired amount of force to be exerted toimmobilize the article or deform the carton walls.

[0021] Referring to FIG. 3, an example is shown of the use of thedensified CHEM foam as a packing material in a second packaging safetyapplication. In this application, the volume factor Y is greater than 1,which results in some amount of free space 33 remaining inside thepackage even after the foam has been fully re-expanded. There istherefore no compressive force applied to the contents 22 of thepackage. For such applications where Y is greater than 1, the personopening the package will immediately see a visual indicator that thepackage interior is not of normal or expected appearance. In thissituation, written warnings of possible heat damage may be printed onthe package wall, included inside the package, or a combination thereof.

[0022] In FIGS. 2 and 3, the original foam volume OV, the densified foamvolume DV, and the free space (OV−DV)*Y available for unrestrained foamexpansion inside the carton are all shown schematically in onedimension. It is to be understood that as used herein, “free space” ismeant to denote substantially one dimension, and that dimension isaligned with the primary direction of the foam expansion. The fact thatthe expanded foam 28 in FIG. 2 will not fill the corner regions of theinterior of the carton does not impact the usefulness of this invention.

[0023] In the simplest embodiment, pre-compacted CHEM structures cansimply be inserted into a carton between the article and the cartonwalls. The structures can also be bonded to the carton walls or to thearticle inside the carton with an adhesive or other means. Sincecompaction volumes to as little as 5% or lower of the expanded volumescan be formed, the compressed insert takes relatively little space andcan be easily fitted into the free space of most conventional packageconfigurations. For example, a typical carton for a medicine vial canhave inside dimensions of about 35×35 mm, and the vial has about a 22.0mm diameter. This leaves a free space of about 6.5 mm on each side. Thecompressed foam insert can be formed as a thin sheet about 0.5 to 1 mmin thickness, which will expand to about 7.0 mm to 10 mm in thickness ifit were not restrained by either the carton wall or vial. Theover-thickness of 0.5 mm to 3.5 mm on one or more sides of the vial(which may be wrapped with product data sheet) exerts sufficientpressure to prevent the vial from being readily removed from the carton.As used herein, over-thickness in FIG. 2 and FIG. 3 is defined as(OV−DV)*(1−Y).

[0024] Note that for packaging systems where the volume factor Y is lessthan 1, the calculated over-thickness is greater than zero, indicatingthat the foam will exert a compressive force on the package contentswhen the foam is exposed to temperatures greater than its Tg. Forpackaging systems where Y is greater than one, the calculatedover-thickness is less than zero, indicating that the package contentswill not be subjected to a compressive force. For packaging systemswhere Y is equal to 1, the calculated over-thickness is zero.

[0025] Test samples were made of thin strips of CHEM material having aglass transition temperature Tg of about 126° F. (52° C.) and anexpanded density of approximately 0.07 g/cm³. Other samples were madewith a CHEM material having a Tg of about 144° F. (63° C.) and anexpanded density of approximately 0.03 g/cm³. The samples, in theircompressed state, were lightly glued to the insides of an insulin vialcarton. The carton, with vial and product information sheets inserted,was gently heated to approximately 10° F. above the foam's respective Tgfor 3 minutes. After allowing the carton to cool to room temperature, avisual inspection showed that the foam had re-expanded to completelyfill the free space in the carton, and unexpectedly, removal of themedicine vial from the foam package was extremely difficult.

[0026]FIG. 4 illustrates a carton with compacted inserts 2 of CHEM foammaterial on the left hand side, and with the foam material 4 re-expandedon the right hand side. In this test, it was found that the vial 6 couldnot be removed from the package without tearing or destroying thepackage.

[0027] In another embodiment of the present invention, the compressedfoam is used as a heat-damage indicator in a panel located within a wallof the carton that can be externally inspected, rather than as an insertinside the carton. In this version, exposure of the carton totemperatures at or above the foam Tg results in the re-expanded foammaterial rupturing the panel outwardly, so that its ruptured state isreadily visible. In this manner, sale, distribution or use of theheat-damaged article can be avoided.

[0028] Referring to FIG. 5, an example of the heat-damage indicatorpanel is shown schematically. The carton has side walls 40 and a toppanel 41 above the article in the carton. The top panel 41 has anaperture and a compressed foam chip DV mounted at its inner surfaceadjacent the top of the article (vial). The aperture in the top panelmay be sealed with a film 41 a, which may be transparent or opaque, toprevent any moisture from getting to the compressed foam chip, or toprevent the chip otherwise becoming damaged or dislodged before itserves its function. When the carton with the packaged article isexposed to a temperature at or above the foam Tg, the foam re-expands toits original volume OV which can be 10× or 20× its densified volume DV.The bulk of the expanded foam causes the film in the aperture to beruptured and the panel surface to be pushed outwardly (dashed lines). Inthis state, it is a clear indication to anyone that the carton has beenexposed to a temperature greater than the temperature that isrecommended for the package contents.

[0029] The use of the thermal memory foam in accordance with the presentinvention provides a clear and distinctive indication that the contentsof the package have been exposed to temperatures greater thanrecommended or considered safe. In the insert mode, the expanded volumeof the foam is used to make the contents difficult to physically remove.The inserts also provide a thermal insulating layer between a heatsource and the package contents, thereby protecting the contents atlesser temperatures which might cause some damage. The inserts may bemade in a variety of shapes, as desired, for example, plates, panels,discs, rings, etc. As long as the inserts have not been expanded, theycan also be reused repeatedly, such as for carrier or delivery packages.If they have been expanded, they can also be re-compacted and reused. Inthe rupture mode, the foam deforms the package walls or ruptures aninspection panel so that the heat-damage indication is externallyvisible.

[0030] The expandable foam materials can be designed and manufactured ina wide range of glass transition temperatures, densified volumes, andoriginal volumes, depending upon the dimensions and configurations ofthe packaging they are to be used with. They can also be made in avariety of cell sizes and colors, or printed or laminated with othermaterials. The thermal memory foam can thus be used as an indicator forheat damage for a wide range of goods and products, includingpharmaceuticals, food, beverages, medical packaging (e.g., vaccines,medicines, body parts), etc. The activation of the foam in a matter of afew minutes is long enough to eliminate short heat transition effects,but long enough to register when enough heat has been applied that coulddamage sensitive contents such as pharmaceuticals and medicines.

[0031] The carton holding the heat sensitive contents shall becontainers of various sizes and shapes, and made from paperboard,plastic, metal or other such materials.

[0032] It is understood that many modifications and variations may bedevised given the above description of the principles of the invention.It is intended that all such modifications and variations be consideredas within the spirit and scope of this invention, as it is defined inthe following claims.

I claim:
 1. A method for packaging an article which containsheat-sensitive contents that may be damaged by exposure to temperaturesabove a predetermined threshold temperature Tt comprising: selecting anopen cellular foam material having a thermal memory characteristic at aglass transition temperature Tg which is approximately equal to orgreater than the predetermined threshold temperature of the contents ofthe article; forming the foam material to an original foamed volume OV;compressing the foam material at an elevated temperature above its glasstransition temperature Tg to a selected densified volume DV; cooling thedensified foam material to a temperature below its Tg to retain it inthe densified state; applying the densified foam material around anarticle in a carton leaving a free space in the carton, such that when atemperature exceeding the glass transition temperature Tg is applied tothe carton with the foam material around the article containing theheat-sensitive contents, the foam material is re-expanded tosubstantially its original volume OV to indicate exposure to atemperature above the predetermined threshold temperature Tt.
 2. Amethod according to claim 1, wherein the free space is equal to thequantity (OV−DV) multiplied by a volume factor Y.
 3. A method accordingto claim 2, wherein the volume factor Y is less than 1.0, such that thefoam material re-expands to a volume exceeding the available free spaceinside the carton, resulting in a compressive force on the article andthe carton, the compressive force being sufficient to deform the cartonso that the deformation is visible externally.
 4. A method according toclaim 2, wherein the volume factor Y is less than 1.0, such that thefoam material re-expands to completely fill the available free spaceinside the carton, resulting in a compressive force on the article, thecompressive force being such that the article cannot be readily removedfrom the carton
 5. A method according to claim 2, wherein the volumefactor Y is equal to or greater than 1.0, such that the foam materialre-expands without restraint and the re-expanded foam material providesa visual indicator of exposure to a temperature equal to or greater thanTt.
 6. A method according to claim 1, wherein the free space is locatedbetween the article and the densified foam material.
 7. A methodaccording to claim 1, wherein the free space is located between a wallof the carton and the densified foam material.
 8. A method according toclaim 6, wherein the densified foam material is in the form of a thinstrip inserted along a wall of the carton.
 9. A method according toclaim 7, wherein the densified foam material is in the form of a thinstrip inserted adjacent to the article.
 10. A method according to claim1, wherein the open cellular foam material is a polyurethane-basedthermoplastic polymer.
 11. A method according to claim 1, wherein theopen cellular foam material is produced from butadiene liquid polymer,an activator and sulfur monochloride.
 12. A method according to claim 1,wherein the re-expanded foam material deforms the carton walls so thatthe deformation is visible externally.
 13. A method according to claim1, wherein the re-expanded foam material presses against the articlewith sufficient force that it cannot be readily removed from the carton.14. A method for packaging an article which contains heat-sensitivecontents that may be damaged by exposure to a temperature above apredetermined threshold temperature Tt comprising: selecting an opencellular foam material having a thermal memory characteristic at a glasstransition temperature Tg which is approximately equal to or greaterthan the predetermined threshold temperature of the contents of thearticle; forming the foam material to an original foamed volume OV;compressing it at an elevated temperature above its glass transitiontemperature Tg to a selected densified volume DV; cooling the densifiedfoam material to a temperature below its Tg to retain it in thedensified state; applying the densified foam material to aheat-damage-indicating panel located within a wall of a carton having aninner surface adjacent the article and an outer surface visibleexternally of the carton which is rupturable by the re-expanded foammaterial applied to the heat-damage-indicating panel, such that when atemperature exceeding the glass transition temperature Tg is applied tothe carton, the foam material in the heat-damage-indicating panel isre-expanded to substantially its original volume OV and thereby rupturesthe outer surface of the panel to indicate that the contents of thearticle may be heat-damaged.
 15. A method according to claim 14, whereinthe open cellular foam material is a polyurethane-based thermoplasticpolymer.
 16. A method according to claim 14, wherein the open cellularfoam material is produced from butadiene liquid polymer, an activatorand sulfur monochloride.
 17. A method according to claim 14, wherein thedensified foam material is in the form of a thin chip mounted to aninternal surface of the heat-damage-indicating panel of the cartonadjacent the contents, and the panel has an aperture through which there-expanded foam material pushes outwardly to provide an externalindication of heat damage.
 18. An indicator for heat damage to anarticle which contains heat-sensitive contents, comprising: the cartonhaving a panel formed on a wall thereof in which a heat-detectingelement is mounted, said element being open cellular foam materialhaving a thermal memory characteristic at a glass transition temperatureTg which is approximately equal to or greater than a predeterminedthreshold temperature Tt of the contents of the carton, wherein foammaterial of the heat detecting element has an original foamed volume OVand is compressed to a densified volume DV; and the panel of the cartonhaving an inner surface mounting the heat-detecting element adjacent thearticle and an outer surface visible externally of the carton which isrupturable by the foam material when re-expanded by a temperatureexceeding the glass transition temperature Tg of the foam material. 19.An indicator for heat damage to a packaged article according to claim18, wherein the panel has an aperture in its external surface and theheat-detecting element in the form of a compressed foam chip mounted atits inner surface adjacent the article.
 20. An indicator for heat damageto a packaged article according to claim 18, wherein the aperture in thepanel is sealed with a transparent film.
 21. An indicator for heatdamage to a packaged article according to claim 18, wherein the aperturein the panel is sealed with a non-transparent, opaque film.